The present invention relates to a wheel hub clutch assembly adapted for use in a four-wheel drive vehicle. More particularly, the present invention relates to a wheel hub clutch assembly for automatically effecting engagement between a drive axle and a wheel hub in response to rotation of the drive axle.
One such wheel hub clutch assembly as described above is set forth in U.S. patent application Ser. No. 06/524,667 filed on Aug. 19, 1983 now U.S. Pat. No. 4,538,714. The wheel hub clutch assembly disclosed in that application comprises a cylindrical body secured to an outer end of a wheel hub, and an inner sleeve member fixedly mounted on an outer projection of the axle by a splined connection. The cylindrical body is integrally formed at its inner peripheral wall with first clutch teeth in the form of an internal spline. In the interior of the cylindrical body, a clutch member, a cam ring, a cam follower ring, a cylindrical connecting member and coil springs are assembled on the sleeve member. A brake member is assembled within a drum which is mounted on an outer end of an axle tube. The cam ring is further provided at its outer end face with a cylindrical portion which is formed with a root, a pair of straight rise cam faces, a pair of flat cam faces and a pair of axial projections upon which a radial projection of the cam follower ring abuts.
In initial operation of the wheel hub clutch assembly, the cam follower ring is axially moved toward the clutch member against one of the coil springs by engagement with one of the straight rise cam faces. The cam follower ring is retained in its displaced position by engagement with one of the flat cam faces.
However, one problem with such a wheel hub clutch assembly is that it may not be easily disengaged between the first clutch teeth and the clutch member. This is a result of the fact that an axial displacement of the clutch member is nearly directly proportional to the power, as shown in FIG. 6, due to the straight rise cam faces.